Borate cross-linking solutions

ABSTRACT

A cross-linking system using boron alpha-hydroxy carboxylic acid salts is shown for use in a water based well treating fluid. The cross-linker will gel the water based fluid usually after a delay at a relatively neutral pH. The cross-linker is provided as a concentrated stable solution containing borate ion as boric acid in a concentration of from less than 1% up to 25% by weight. The cross-linking solution additionally may contain from 1% to 10% of EDTA and/or Glycerine, however, without these additives the cross-linking solution is stable through temperature changes and freeze-and-thaw cycles. Water based fracturing fluid is shown using galactomannan guar polymers, hydroxypropyl guar polymers or derivatives thereof.

This is a division, of application Ser. No. 07/705,605 filed May 24,1991 now U.S. Pat. No. 5,160,445.

FIELD OF THE INVENTION

The invention relates to various solutions containing borate ions foruse primarily in aqueous, galactomannan gum polymers, hydroxypropyl guar(HPG) and carboxymethyl hydroxypropyl guar (CMHPG) polymers forcross-linking the polymers and creating delayed cross-linking mechanism.

BACKGROUND OF THE INVENTION

It is well known that boric acid is a very weak, inorganic acid and theborate ion does not exist as such until the pH is sufficiently high toreact with more firmly bound second and third hydrogens. The borate ioncomplexes with many compounds, for example certain polysaccherides likeguar and locust bean gum as well as polyvinyl alcohol. At a high pHabove 8, the borate ion exists and is available to cross-link and causegelling. At lower pH, the borate is tied up by hydrogen and is notavailable for cross-linking, thus gelation caused by borate ion isreversible.

According to Friedman, U.S. Pat. No. 3,800,872, if boric acid or boraxis added to a 1% fully hydrated guar solution, the solution will gel.If, however, the procedure is reversed and one attempts to dissolve guarin a solution containing borax, hydration will not occur. The guar thenappears to be water insoluble and no viscosity increases will bemeasured. The reason for this is that if the borate ion finds two ormore guar molecules close together, there is a fair probability that itwill link them together.

If, on the other hand, the borate gets to the slowly hydrating moleculebefore the guar molecules get close together to link, the intermoleculardistances are too large to be spanned by the small borate ion. Thiscauses the borate to use all its functional points to hook to one guarmolecule shielding it from hydration. If a very dilute guar solution isallowed to fully hydrate and subsequently borated, the solution losesviscosity.

Another way in which borate ions form a complex is with a cis diol wheretwo alcohol groups are on adjacent carbon atoms. If boric acid is addedto a cis diol like glycerol, the resulting chelate holds the borate ionso tightly that the hydrogen becomes relatively labile. This makes astrong acid of boric acid. If a cis diol is added to a borate gel guar,the gel disappears because the diol attracts the borate more stronglythen does the guar. Consequently, this aqueous gelling is a reversibleprocess. Friedman goes on to discuss boric acid or borax as across-linker for aqueous flooding medium for an oil and gas reservoir.

Mondshine, U.S. Pat. No. 4,619,776, discloses that it is well known thatorganic polyhydroxy compounds having hydroxyl groups positioned in thecis-form on adjacent carbon atoms or on carbon atoms in a 1,3-relationship react with borates to form five or six member ringcomplexes. At alkaline pH's of above about 8, these complexes formdididols cross-link complexes. Mondshine goes on to state that suchreversible reactions lead to a valuable reaction with disassociatedborate ions in the presence of polymers having the required hydroxylgroups in a cis-relationship. The reaction is fully reversible withchanges in pH. An aqueous solution of the polymer will gel in thepresence of borate when the solution is made alkaline and will liquifyagain when the pH is lowered below about 8. If the dried powder polymeris added to an alkaline borate solution, it will not hydrate and thickenuntil the pH has dropped below about 8. The critical pH at whichgelation occurs is modified by the concentration of dissolved salts. Theeffect of the dissolved salts is to change the pH at which a sufficientquantity of disassociated boric ions exist in solution to causegelation. The addition of an alkali metal base such as sodium hydroxideenhances the effect of condensed borate such as borax by converting theborax to the disassociated metaborate.

Known polymers which contain an appreciable content of cis-hydroxylgroups are exemplified by guar gum, locust bean gum, dextrin, polyvinylalcohol and derivatives of these polymers. Derivatives tend to reactless with the borate ion as the amount of substituting group in themolecule increases. This results because of the sheer bulk ofsubstituting groups changes the regular alternating and simple numberbranched linear configuration of the molecule and prevents adjacentchains from approaching as closely as before and a substitution ofsecondary cis-hydroxyl positions decreases the number of suchunsubstituted positions available for complexing with the borate ion. Asfurther pointed out by Mondshine, hydraulic fracturing is a widely usedmethod for stimulating petroleum producing subterranean formations andis commonly performed by contacting the formation with a viscousfracturing fluid having particulated solids, widely known as proppingagents, suspended therein applying sufficient pressure to the fracturingfluid to open a fracture in the subterranean formation and maintainingthis pressure while injecting the fracturing fluid into the fracture ata sufficient rate to extend the fracture into the formation. When thepressure is reduced, the propping agents within the fracture prevent thecomplete closure of the fracture.

The properties that a fracturing fluid should possess are, among others,a low leak-off rate, the ability to carry a propping agent, low pumpingfriction loss and it should be easy to remove from the formation. Lowleak-off rate is a property that permits the fluid to physically openthe fracture and one that controls its areal extent. The ability of thefluid to suspend a propping agent is controlled by additions.Essentially, this property of the fluid is dependent upon the viscosityand density of the fluid and upon its velocity. Friction reducingadditives are added to fracturing fluids to reduce pumping loss due tofriction by suppression of turbulence in the fluid. To achieve maximumbenefit from fracturing, the fracturing fluid must be removed from theformation. This is particularly true with the viscous fracturing fluids.Most such viscous fluids have built in breaker systems that reduce theviscosity gels to low viscosity solutions upon exposure to temperaturesand pressures existing in the formation. When the viscosity is lowered,the fracturing fluid may readily be produced from the formation.Mondshine states that he has found that superior guar containinghydraulic fracturing fluids having enhanced thermal stability anddecreased leak-off rate can be obtained utilizing 1/2 to 15 kilogramsper cubic meter of sparingly soluble borate having a slow solubilityrate to provide sufficient borate ions to cross-link the guar polymer,raise the pH, and provide a reserve of available borate ions tocross-link the polymer at high temperatures. Mondshine goes on tosuggest that alkaline earth metal borates or alkali metal alkaline earthmetal borates have unique solubility characteristics which enable themto be used in the control cross-linking of aqueous systems containingguar polymers. The rate of cross-linking can be controlled by suitableadjustment of one or more of the following variables: initial pH of theaqueous solutions system, relative concentration of one or more of thesparingly soluble borates, the temperature of the borates, temperatureof the aqueous system and particle size of the borate. In the patent,the inventor further describes a series of sparingly soluble borates foruse in fracturing fluids.

On occasion, it is desirous to temporarily seal or plug a permeableformation located in a subterranean oil and gas formation having a borehole therein. This may be done for several purposes such as, forexample, so that other less permeable zones can be treated in somemanner, i.e. fractured, acidized, etc. Many methods and compositionshave been employed for temporarily plugging or sealing the openings orpassageways located in such formations. Nimerick, U.S. Pat. No.3,766,984 discusses at length the use of gels such as cross-linkpolysaccherides, and Nimerick suggests the use of an aqueous slurringcomposition containing a portion of the constituents of a granulatedcomposition comprised of a galactomannan gum which has been treated withhydrophobing agent to render the gum hydrophobic (less hydrophilic thannormal) when disbursed in an aqueous solution having a pH of at least7.5, a pH control agent and a water soluble organic polymer suspendingagent. Optionally, a degrading agent for a hydrated form of the gumand/or a cross-linking agent for hydrated gum and/or hydration agentscan be employed.

Skagerberg, U.S. Pat. No. 3,794,115 describes a relatively lowconcentration of polymer which can be pumped through the system withoutusing excessive high pressure and goes on to list numerous polymerssuitable for use in aqueous solutions for forming bore hole plugs andfurther suggests the use of borax glass as one of a number ofcross-linking agents including antimony and chromic ions.

SUMMARY OF THE INVENTION

I have now found that concentrated, stable solutions of boric acid canbe prepared through an in-situ formation of an alkali metal or ammoniumsalt of an alpha-hydroxy carboxylic acid such as citric, lactic andtartaric, in an aqueous, boric acid slurry. This invention involvesslurring relatively large quantities of boric acid or borax solids in anaqueous solution of the alpha-hydroxy carboxylic acid followed by theaddition of sodium, potassium or ammonium hydroxide (for the in-situformation of the acid salt) till a pH of at least 6.5 is established.This method of preparing produces a clear, stable solution of boric acidwith an almost neutral pH. Other substances useful in this invention toincrease or establish the pH are: sodium, potassium, ammonium carbonateor bicarbonate and water-soluble amines and amine derivatives.Experimental results indicate good stability of these solution productsfrom this new method of preparation on aging and through freeze and thawcycles. Using this invention, boric acid cross-linkers can be made in anaqueous, stable and neutral solution at concentrations from less than 1%of up to 25% boric acid by varying the boric acid to alpha-hydroxycarboxylic acid molar ratios. These solutions have been demonstrated tobe stable in excess of six months and cycle through at least threefreeze and thaw cycles.

Thus, I have discovered these stable, concentrated boric acid solutionsprepared in accordance with the present invention have the uniquecharacteristic of cross-linking neutral-pH guar and substituted guar gumsolutions providing delayed cross-linking action, without the additionof buffers to the frac fluid prior to the cross-linkers addition.

Thus, I have discovered a new borate ion solution which remains stableover an extended period of time and through temperature extremes at arelatively neutral pH which can be used with the numerous guar and guarderivatives solutions.

I believe the neutral-pH cross-linking occurs as a result of theformation of pseudo cationic bonding sites on the polymer "backbone".Using sodium boron lactate, the proposed type of bonding can bepresented by the following steps: ##STR1## As the sodium ion approachesthe hydroxy group on the polymer, an electrostatic bond occurs with theoxygen of the hydroxyl group on the polymer at 1) forming a pseudocationic bonding site at 2). The carboxyl group (COO) approaches thispseudo cationic bonding site and the carboxyl group and the hydroxylgroup share the sodium cation.

This pseudo cationic electrostatic bonding gels the polymer usuallyafter a period of delay. In addition, as or if the pH is increased, theusual boron type of cross-linking occurs, as well as continue bonding ofcarboxyl and sodium at the pseudo cationic bonding site.

DESCRIPTION OF PREFERRED EMBODIMENT

Concentrated, stable solutions of boric acid were prepared through anin-situ formation of an alkali metal or ammonium salt of analpha-hydroxy carboxylic acid such as citric, lactic, and tartaric in anaqueous boric acid slurry. This invention involves slurring relativelylarge quantities of boric acid or borax solids in a concentrated aqueoussolution of the alpha-hydroxy carboxylic acid, followed by the additionof sodium, potassium, or ammonium hydroxide (for the in-situ formationof the acid salt) till a pH of at least 6.5 is established. This methodof preparation produces a clear, stable solution of boric acid withalmost a neutral pH. Experimental results indicated good stability ofthese solution products from this new method of preparation, on agingand/or freeze-and-thaw cycles.

EXAMPLE 1

The following example illustrates the new method of preparation: 600 gmof 50% citric acid was diluted with 840 gm of water. Then 400 gm ofgranular boric acid was slurried in the aqueous citric acid solution.408 gm of 50% sodium hydroxide was gradually added to the slurry withcontinuous mixing. Heat was generated as a result of neutralizing thecitric acid with 50% sodium hydroxide. The boric acid in the slurrygradually dissolved while NaOH was being added. When the addition ofNaOH was completed, all of the boric acid dissolved, and a neutral,stable solution of boric acid was obtained. Similar results wereobtained when granular boric acid was slurried initially in the water,followed by the addition of the 50% citric acid.

In the above example, lactic acid or tartaric acid can be substitutedfor citric acid. Potassium or ammonium hydroxide can be substituted forsodium hydroxide to obtain similar stable products. In the aboveexample, the boric acid concentration in the final solution product was17.8% and the product was stable for at least six months and/or at leastthree freeze-and-thaw cycles. Using this new method, boric acid can bemade in an aqueous, stable and neutral solution form at a concentrationof up to 25% through varying the B(OH)₃ : alpha-hydroxy carboxylic acid:hydroxide molar ratios. These stable boric acid solutions can beprepared through the in-situ formation of any or a combination of thefollowing salts:

Sodium Citrate

Sodium Lactate

Sodium Tartrate

Potassium Citrate

Potassium Lactate

Potassium Tartrate

Ammonium Citrate

Ammonium Lactate

Ammonium Tartrate

Laboratory experimental results indicate that the concentrated boricacid solutions prepared using these new methods are effective as delayedcross-linking agents for guar and HPG solutions. This delayed action canbe utilized in fracturing fluids in the oil field and similarrheological applications.

In another embodiment of the invention, four different products wereprepared using similar techniques. The first product wasself-stabilized. The second contains approximately 5%ethylenediaminetetraacetic acid salt. The third contains approximately5% glycerine. The fourth contains approximately 5%ethylenediaminetetraacetic acid salt and 5% glycerine for furtherstabilization towards aging and freeze-and-thaw cycles. The percentageof EDTA may be between 1% and 10% and the glycerine may be between 1%and 10%. Wherever hereinafter EDTA is used, it is meant the salt ofethylenediaminetetraacetic acid. The initial objective of making theseproducts was to prepare stable, soluble concentrated boric acidsolutions. Their unique characteristics of cross-linking neutral-pH guarsolutions, and their delayed cross-linking action was discovered.

EXAMPLES II THROUGH V

II. Preparation of sodium-boron citrate from boric acid (BXL).

a.) Ingredients

500 g of 50% citric acid

400 g of boric acid

735 g of distilled water (varies to yield 20% B(OH)₃ in the product)

370 g of 50% NaOH solution (or the amount required to raise the pH to6.0-6.5)

Batch wt.=2005 g

B (OH)₃ in product=20.0%

b.) Procedure

1. 500 g of 50% citric acid was diluted with 735 g of water.

2. 400 g of boric acid was added and the batch was mixed for two hours.

3. 370 g of 50% NaOH was gradually added to the reaction batch toestablish a pH of 6.0-6.5 in the product. Mix for thirty minutes and wasreadjusted to pH to 6.0-6.5 with 50% NaOH.

III. Preparation of Sodium Boron Citrate containing EDTA (BXL-EDTA).

a.) Ingredients

500 g of 50% citric acid

641 g of water (or the amount to yield 20% B (OH)₃ in the product)

370 g of 50% NaOH (or the amount to establish a pH of 6.0-6.5 in thefinal product)

400 g of boric acid

94 g of EDTA (ethylene diamine tetracetic acid) sodium salt

Batch Weight=2005 g

B (OH)₃ in product=20.0%

EDTA in product=4.7%

b.) Procedure

1. 500 g of 50% citric acid was diluted with 641 g of water.

2. 400 g of boric acid was added, and batch was mixed for two hours.

3. 94 g of EDTA was added and mixed for thirty minutes.

4. 370 g of 50% NaOH solution (the amount required to raise the pH to6.0-6.5) was added and mixed for thirty minutes. The batch pH was thenchecked and readjusted to 6.0-6.5 with 50% NaOH, as needed.

IV. Preparation of Sodium Boron Citrate containing glycerine (BXL-GLY).

a.) Ingredients

500 g of 50% citric acid

641 g of water (or the amount to yield 20% B (OH)₃ in the product)

370 g of 50% NaOH (or the amount to establish a pH of 6.0-6.5 in thefinal product)

400 g of boric acid

94 g of glycerine

Batch Weight=2005 g

B (OH)₃ in product=20.0%

Glycerine in product=4.7%

b.) Procedure

1. 500 g of 50% citric acid was diluted with 641 g of water.

2. 400 g of boric acid was added, and batch was mixed for two hours.

3. 94 g of glycerine was added and mixed for thirty minutes.

4. 370 g of 50% NaOH solution (the amount required to raise the pH to6.0-6.5) was added and mixed for thirty minutes. The batch pH was thenchecked and readjusted to 6.0-6.5 with 50% NaOH, as needed.

V. Preparation of Sodium Boron Citrate containing EDTA and glycerine(BXL-EDTA/GLY).

a.) Ingredients

500 g of 50% citric acid

370 g of 50% NaOH solution

547 g of water

94 g of EDTA

94 g of glycerine

400 g of boric acid

Batch weight=2005 g

B (OH)₃ in product=20.0%

EDTA in product=4.7%

glycerine in product=4.7%

b.) Procedure

1. 500 g of 50% citric acid was diluted with 547 g of distilled water.

2. 400 g of boric acid was added, and the batch was mixed for two hours.370 g of 50% NaOH was gradually added with mixing to the reaction batch.

3. 94 g of glycerine was added, and the batch was mixed for thirtyminutes.

4. 94 g of EDTA was added, and the batch mixed for thirty minutes.

5. 370 g of 50% NaOH was gradually added (the amount required to raisethe pH to 6.0-6.5, and the batch was mixed for thirty minutes.

The four products were stable on aging for at least 6 months to 1 yearand through at least three freeze-and-thaw cycles.

The first product (Example II) and fourth product (Example V), sodiumboron citrate and sodium boron citrate which contains EDTA andglycerine, respectively, were given the identification BXL andBXL-EDTA/GLY, respectively. These products were evaluated as delayedcross-linking agents for guar solutions under various cross-linkingconditions. Usually, the galactomannan gum polymers such as guar gum,hydroxypropyl guar (HPG) and carboxymethyl hydroxypropyl polymers aredissolved in water to form the base gel. The ratio is between 20 to 60pounds of polymer per 1000 gallons of water. Thus, the polymers have aconcentration between 0.24 to 0.72 percent by weight. Optionally, 2% KCIis added as a clay stabilizer and optionally, a buffer is added. Thecross-linker in frac fluids is usually about one to three gallons perthousand gallons of frac fluid. In the particular evaluation following,the base gel guar contained 40 pounds of guar per 1000 gallons of water.

Evaluation of BXL as a delayed cross-linking agent

The effectiveness of BXL as a delayed cross-linking agent at almostneutral pH, and at various loadings was investigated. The results in thetests set forth herein were obtained using an overhead mixer with therheostat setting at 60 (high voltage). The cross-linking time wasmeasured from the second the cross-linker was added to the second atwhich the gel started to climb the shaft. The gel strength was visuallyevaluated by the gel appearance and its behavior when poured out of thecontainer. 750 ml of the base gel was used in every test. The pH of thebase gel varied between 6.0-7 0 in various preparations. The product hasshown a desirable and unusual behavior of slow cross-linking of guarsolutions at almost neutral pH. The following data in Table I shows thevariation of the cross-linking time with the BXL loading at almostneutral pH. Through several preparations, pH of BXL varied between7.0-7.5. Later work had proved that higher stability of BXL and slowercross-linking action can be obtained by preparing the product at a pH of6.0-6.5.

                  TABLE I                                                         ______________________________________                                                                          COM-                                                 PH IMMEDIATELY           MENTS                                                AFTER THE      CROSS-    ON GEL                                      LOADING  ADDITION AND   LINKING   STRENGTH                                    Gal/1000 gal                                                                           MIXING OF      TIME      (at room                                    OF BXL   BXL            min    sec  temp.)                                    ______________________________________                                        2/3      7.2            04     01   The produced                                                                  gel was weak                              1        7.3            02     25   The produced                                                                  gel was weak                              11/3     7.3            01     59   The produced                                                                  gel was weak                              22/3     7.5            01     28   The produced                                                                  gel was weak                              ______________________________________                                    

The obtained gels were relatively weak compared to conventional borategels. Higher loadings of BXL than 1-2/3 gal/1000 gal (2-3 gal) producedsatisfactory gels.

Evaluation of BXL-EDTA/GLY as a delayed cross-linking agent

The effectiveness of BXL-EDTA/GLY as a delayed cross-linking agent atalmost neutral pH, and at various loadings was investigated. The resultsin the tests set forth herein were obtained using an over-head mixerwith the rheostat setting at 60 (high voltage). The cross-linking timewas measured from the second the cross-linker was added to the second atwhich the gel started to climb the shaft. The gel strength was visuallyevaluated by the gel appearance and its behavior when poured out of thecontainer. 750 ml of the base gel was used in every test. The pH of thebase gel varied between 6.0-7.0 in various preparations. The product hasshown a desirable and unusual behavior of slow cross-linking of guarsolutions at almost neutral pH. The following data in Table II shows thevariation of the cross-linking time with the BXL-EDTA/GLY loading atalmost neutral pH. Through several preparations, pH of BXL-EDTA/GLYvaried between 7.0-7.5. Later work had proved that higher stability ofBXL-EDTA/GLY and slower cross-linking action can be obtained bypreparing the product at a pH of 6.0-6.5.

                  TABLE II                                                        ______________________________________                                                 PH IMMEDIATELY           COM-                                                 AFTER THE                MENTS                                       LOADING  ADDITION AND   CROSS-    ON GEL                                      Gal/1000 gal                                                                           MIXING OF      LINKING   STRENGTH                                    OF BXL-  BXL-EDTA       TIME      (at room)                                   EDTA/GLY GLY            min    sec  temp.)                                    ______________________________________                                        2/3      7.2            04     01   The produced                                                                  gel was weak                              1        7.3            02     25   The produced                                                                  gel was weak                              11/3     7.3            01     59   The produced                                                                  gel was weak                              22/3     7.5            01     28   The produced                                                                  gel was weak                              ______________________________________                                    

The obtained gels were relatively weak compared to conventional borategels. Higher loadings of BXL-EDTA/GLY than 1-2/3 gal/1000 gal (2-3 gals)produced satisfactory gels.

Effects of different chemicals on the cross-linking time and gelstrength using BXL-EDTA/GLY

(a) 10% soda ash solution

The loading of 1 gal/1000 gal of BXL-EDTA/BLY was used in this study.The loading of 10% Na₂ CO₃ solution was varied, and the correspondingcross-linking time was measured. The results obtained are listed belowin Table III.

                  TABLE III                                                       ______________________________________                                                  PH AFTER                                                            10% SODIUM                                                                              ADDING                                                              CARBONATE CROSS-LINKER CROSS-                                                 LOADING   SODIUM       LINKING                                                gal/1000  CARBONATE    TIME                                                   gal       SOLUTION     min    sec  COMMENTS                                   ______________________________________                                        0.0       7.3          2      25   weak gel                                   1/3       8.1          1      24   medium                                                                        strength gel                               2/3       9.0          0      55   stronger than                                                                 above                                      1         9.3          1       6   stronger than                                                                 above                                      11/3      9.5          1       5   medium                                                                        strength gel                               22/3      9.7          1      12   medium                                                                        strength gel                               ______________________________________                                    

Gradual increase of the loading of 10% Na₂ CO₃ solution to one gal/1000gal caused higher pH in the base gel. This resulted in shortercross-linking time and stronger gels. Some of BXL-EDTA/GLY delayedaction must be traded off to obtain usable gels. Based on the obtainedresults, increasing the soda ash solution loading to over one gal/1000gal has very little effect on the cross-linking time, and weaker gelsare produced.

(b) 10% Sodium Diacetate Solution

Ten percent solution of sodium diacetate was prepared and used in thisinvestigation. One gal/1000 gal of BXL-EDTA/GLY was utilized in all thetests. The results obtained are listed in the following table IV.

                  TABLE IV                                                        ______________________________________                                        gal/1000 gal                                                                            PH AFTER                                                            OF 10%    DIACETATE    CROSS-                                                 SODIUM    IS ADDED     LINKING                                                DIACETATE (BEFORE BXL- TIME                                                   SOLUTION  EDTA/GLY     min    sec  COMMENTS                                   ______________________________________                                        0.0       7.3          2      25   weak gel                                   1/3       7.8          3      25   weaker gel                                 2/3       7.8          9      14   weaker gel                                 1         7.3          No vortex very weak                                                           closure up                                                                              gel                                                                 to 15                                                                         minutes                                                ______________________________________                                    

The addition of sodium diacetate solution delays the cross-linkingaction of BXL-EDTA/GLY. Weaker gels are produced when sodium diacetateis used, to further delay the cross-linking action of BXL-EDTA/GLY.Higher loadings than 1 gal/1000 gal of BXL-EDTA/GLY are required toproduce usable gels, at pH 7.0-7.8, at room temperature.

The ensuing examples describe preparation of other boron alpha hydroxycarboxylic acid salt solutions. These solutions provide similar resultsas the previous solutions.

EXAMPLES VI THROUGH IX

VI. Using Lactic Acid

(i) 364 gm of 88% lactic acid is diluted with 236 gm of distilled water;

(ii) 200 gm of granular boric acid is added and mixed to obtain auniform slurry;

(iii) 48 gm of ethylenediaminetetraacetic acid sodium salt is added andmixed in the reaction batch;

(iv) 48 gm of glycerine is added and mixed in the reaction batch;

(v) 275 gm of 50% sodium hydroxide solution is gradually added whilemixing;

(vi) 322 gm of water was added and mixed in the batch.

The obtained product was a clear and stable solution. It has a pH of 7.5and it contains 13.4 B(OH)3.

VII Using Tartaric Acid

(i) 175 gm of granular tartaric acid is dissolved in 329 gm of distilledwater;

(ii) 200 gm of boric acid was added and mixed to obtain a uniformslurry;

(iii) 48 gm of ethylenediamine tetracen acid sodium salt was added andmixed in the reaction batch;

(iv) 48 gm of glycerine was added and mixed in the reaction batch;

(v) 215 gm of 50% sodium hydroxide solution was gradually added, whilemixing;

(vi) 158 gm of distilled water was added and mixed in the reactionbatch.

The obtained product was a clear and stable solution. It has a pH of 7.5and it contains 17.1% B(OH)₃.

VIII. Using Ammonium Hydroxide Instead of Sodium Hydroxide

(i) 175 gm of granular tartaric acid is dissolved in 329 gm of distilledwater;

(ii) 200 gm of boric acid was added and mixed to obtain a uniformslurry;

(iii) 48 g of ethylenediamine tetracetic acid sodium salt was added andmixed in the reaction batch;

(iv) 48 gm of glycerine was added and mixed in the reaction batch;

(v) 326 gm of concentrated ammonium hydroxide solution (28% NH₃) wasgradually added, while mixing.

The obtained solution product was clear and stable. It has a pH of 7.2and it contains 17.8% B(OH)₃.

IX. Using Borax Instead of boric acid

(i) dilute 364.3 gm of 88% lactic acid with 235.7 gm of distilled water;

(ii) slurry 308.4 gm of borax (36.5%, B₂ O₃) and mix for 10 minutes;

(iii) add 47.6 gm of ethylenediamine tetracetic acid sodium salt and mixin the reaction batch;

(iv) add 47.6 gm of glycerine and mix in the reaction batch;

(v) gradually add 81 gm of 50% sodium hydroxide solution and mix in thereaction batch.

The obtained product was clear and stable. It has a pH of 7.5 and itcontains 18.4% B (OH)₃.

What is claimed is:
 1. Method of preparing an aqueous boron crosslinkingcompound comprising:Reacting boric acid in an aqueous media with analpha hydroxy carboxylic acid having a concentration of from 1% to 25%by weight boron measured as boric acid; Neutralizing the alpha hydroxycarboxylic acid with sodium, potassium or ammonium hydroxides, orammonium carbonate, ammonium bicarbonate, or water soluble amines toform boron alpha hydroxy carboxylic acid salt with a pH in the range of6.0 to 7.5, whereby the crosslinking compound, when mixed with aqueoustreating fluids, establishes a cationic bonding site on the polymer inwhich the carboxy group and the hydroxyl group of the polymer share thecorresponding cation.
 2. Method of preparing an aqueous boroncrosslinking compound comprising:Reacting boric acid in an aqueous mediawith an alpha hydroxy carboxylic acid having a molar ratio of alphahydroxy carboxylic acid to boron of from 0.1-10.0 to 1.0; Neutralizingthe alpha hydroxy carboxylic acid with sodium, potassium or ammoniumhydroxides, or ammonium carbonate, ammonium bicarbonate, or watersoluble amines to form boron alpha hydroxy carboxylic acid salt with apH in the range of 6.0 to 7.5, whereby the crosslinking compound, whenmixed with aqueous treating fluids, establishes a cationic bonding siteon the polymer in which the carboxy group and the hydroxyl group of thepolymer share the corresponding cation.
 3. Method of preparing anaqueous boron cross-linking compound comprising:Reacting boric acid inan aqueous media with an alpha hydroxy carboxylic acid having aconcentration of from 1% to about 25% by weight boron measured as boricacid; Neutralizing the alpha hydroxy carboxylic acid with sodium,potassium or ammonium hydroxides, or ammonium carbonate, ammoniumbicarbonate, or water soluble amines to obtain a clear stable solutionof boron alpha hydroxy carboxylic acid salt with a pH in the range of6.0 to 7.5.
 4. A composition made in accordance with the method of claim3.
 5. The method of claim 3 wherein said alpha hydroxy carboxylic acidis citric acid, lactic acid or tartaric acid.
 6. The method of claim 3wherein the boric acid or boric acid equivalent of borate ion is in aconcentration from 10% to 20% by weight.
 7. The method of claim 3wherein during the neutralizing step sodium or potassium hydroxide isused.
 8. The method of claim 3 wherein 1% to 10% by weight ofethylenediaminetetraacetic acid is added.
 9. The method of claim 3wherein 1% to 10% by weight of glycerine is added.
 10. The method ofclaim 3 wherein 1% to 10% by weight of ethylenediaminetetraacetic acidand glycerine are added.